1. Field of the Invention
The present invention relates to an original image reading device and an image processing apparatus, and more particularly to an original image reading device and an image processing apparatus having said device for optically reading image information of an original document and detachably mounted on an image information processing apparatus such as a facsimile apparatus, an image scanner or the like.
2. Related Background Art
Requirements for smaller dimension, lower weight and lower cost have become stronger in recent years in the field of image information processing apparatus, such as facsimile apparatus, image scanner or the like. For the facsimile apparatus in particular, there have emerged various requirements for the design and functions, in addition to the above-mentioned ones, following the expansion of market including so-called home facsimile for personal use.
For the original image reading device to be incorporated in such image information processing apparatus for optically reading the image information of the original document, there have been employed a reduction reading system utilizing a line sensor such as a CCD and a reduction optical system; a contact reading system utilizing a line sensor of a length equal to the width of the original, an equal-magnification optical system such as a condensing fiber lens array and a light source such as an LED array, all integrally assembled in a frame; and a complete contact reading system utilizing a line sensor and a light source integrally assembled in a frame, without the lens array, wherein the line sensor is maintained close to the original for directly reading the original image.
An example of such original image reading device is schematically illustrated in FIGS. 1 and 2 which are respectively a cross-sectional view and a schematic perspective view for the original image reading device.
1 is a line sensor as image reading means for optically reading the image of an original P. 13 is an automatic sheet feeding unit consisting of a separating member 11 and a sheet supplying roller 12, for separating and feeding the originals P one by one toward said line sensor 1, even if a plurality of originals are provided, by pressing the separating member 11 toward the sheet supplying roller 12 side with an appropriate force. 2 is a transport (pressure) roller as transporting means having the features of original transporting means for transporting the original P as well as original contacting means for pressing and contacting the fed original P to a reading position 4 of the line sensor 1.
However, as the functions of original transport means and original contacting means are performed by a transport roller in the original image reading device, as shown in FIG. 1, the following drawbacks may result, according to a view of the inventors.
(1) In order to maintain the original in close contact with the line sensor for reading the original image by said line sensor, the transport roller has to be as long as the line sensor or the reading width of the original. Therefore the local unevenness in the transporting power results from the planarity of the reading face of the line sensor, eventually causing skewed advancement of the original.
(2) The transportation of the original in contact with the reading face of the line sensor increases the load on a motor for driving the transport roller, thus eventually leading to heat generation or control abnormality in said motor. Therefore, for achieving stable transportation of the original, there is required a large motor, which becomes an obstacle in compactization and weight reduction of the device.
(3) An original eventually fed in skewed state tends to become more skewed in the course of transportation, as will be explained in the following with reference to FIG. 3.
FIG. 3 is a schematic plan view from above the image reading device shown in FIGS. 1 and 2, wherein the line sensor is not illuminated but is positioned behind the transport roller 2.
When an original P is fed in a skewed state in the automatic sheet feeding unit 13 as shown in FIG. 3A, it is advanced to the transport roller 2, as shown in FIG. 3B, by the transporting force (a) indicated by an arrow. Then, as a part of the original P is pinched between the transport roller 2 and the line sensor as shown in FIG. 3C, said part is subjected to a transportion force (b) of the transport roller 102, indicated by an arrow. In general, the peripheral speed of the feed roller (not shown in the Figure) of the automatic sheet feeding unit 13 is selected somewhat smaller than that of the transport roller 2. Consequently a load (c) indicated by an arrow is generated in a direction opposite to the transport direction of the original, due to a difference in peripheral speed and a load induced by the frictional member, and a rotating force (d), also indicated by an arrow, is generated by the aforementioned transporting force (b) and the load (c), thus causing an increased skew in the original P.
For a demand for a smaller, lighter and less expensive image reading device which is increasingly sought in recent years, as above described, it is said that a construction as shown in FIG. 1 is insufficient, and there are left many technical problems to be solved. These points especially brought about some problems in handling a lensless complete contact type image sensor which can be most compactly fabricated.
And there are still left technical problems for sufficiently meeting the requirements of realizing the demand for a smaller, lighter and less expensive image reading device in recent years.
However, in order to meet requirements for a compact, lightweight, and inexpensive structure, and diversified designs and functions of the image information processing apparatus, the following technical subjects remain unsolved in the conventional image reading device and the image information processing apparatus.
(1) As the apparatus is rendered compact and lightweight, it is difficult to assure assembling position precision. As a result, parts precision must be further improved, thus preventing the manufacture of an inexpensive apparatus.
(1-1) In the conventional image information processing apparatus, since various components are integrally locked on the main body frame, the main body frame assures rigidity of the image information processing apparatus. Therefore, as the apparatus is rendered compact and lightweight, the rigidity of the main body frame is decreased, thus impairing assembling position precision of the respective components. In particular, a decrease in rigidity of the main body frame impairs positional precision between the original image reading device and the platen roller, thus degrading image reading performance, and original convey performance.
(1-2) In order to realize a compact, lightweight apparatus, for example, the dimensions of a gear module are decreased to decrease the gear diameter. In this case, precision of the distance between the centers of gears must be further improved. As a result, it is difficult to reduce parts cost.
(2) Loads upon changes in design and function are considerable, and prevent the manufacture of an inexpensive apparatus.
(2-1) In the conventional image information processing apparatus, since various components are integrally locked on the main body frame, the shape of the main body frame determines the design of the product. Therefore, when the design is changed, the shape of the main body frame must be changed first, and the design load, cost of, e.g., molds, and cost upon a change in production equipment prevent the manufacture of an inexpensive image information processing apparatus.
(2-2) When the functions of the image information processing apparatus are changed, various loads prevent the manufacture of an inexpensive image information processing apparatus like in the change in design.
(3) Replacement and repair are not easy when a defect or malfunction is found.
(3-1) In consideration of the production process of the image information processing apparatus, after components mounting the original image reading device are assembled on the main body frame of the image information processing apparatus, the function check test of the image information apparatus is conducted. As a result of the test, for example, a defect is found in the original image reading device. Other assembled components must be disassembled from the main body frame, and the original image reading device must be replaced or repaired. Furthermore, the original image reading device must be assembled on the main body frame again, and then, adjustment must be performed.
(3-2) For example, when the original image reading device malfunctions during use of the image information processing apparatus, the original image reading device must be disassembled from the main body frame of the image information processing apparatus together with other components, and must be replaced or repaired. Furthermore, the original image reading device must be assembled on the main body frame again, and then, adjustment must be performed.
In particular, in the contact reading system, since the focal depth is relatively shallow, an original and the reading surface must be precisely aligned. In this case, when the platen roller 2 and the reading device 1 are independently locked on the main body frame 106 of the apparatus like in the conventional apparatus, it is difficult to align the roller 2 with the reading surface of the reading device 1, thus undesirably prolonging an assembling time of the overall apparatus.